Orthogonal frequency division multiplexing (OFDM) systems have good anti-attenuation performance and therefore are widely used in existing wireless communications systems. A time-domain signal of an OFDM system is generated by means of an inverse fast Fourier transform (IFFT) operation. The multiple-input multiple-output (MIMO) technology can significantly increase a channel capacity and therefore is also a commonly used technology for modern wireless communications. Many existing communications systems, for example, Long Term Evolution (LTE) and 802.11 communications systems, use both OFDM and MIMO. In this case, for sending of a data stream, a common implementation manner is as follows: first performing precoding processing on each coded and modulated data stream to obtain a frequency-domain data stream for each antenna, and then separately performing IFFT processing on the frequency-domain data stream for each antenna to obtain a time-domain signal on each antenna. For the foregoing implementation solution, a quantity of times of IFFT processing that needs to be performed is equal to a quantity of transmit antennas. Especially in an LSM system, because a quantity of antennas increases sharply, a quantity of times of IFFT processing that needs to be performed also increases sharply. Therefore, a large quantity of hardware resources need to be used, or a total runtime of an IFFT module needs to be increased, thereby reducing operating efficiency of the system.